Abstract: Objective To quantitatively observe the actual levels of 4977 bp and 3895 bp mitochondrial DNA(mtDNA) deletion in healthy human skin of different age, and to explore their relationship with intrinsic aging and photoaging. Methods Seventy-one samples of skin tissue were obtained from healthy volunteers, including 40 samples from UV-protected areas （buttock, thigh, waist or abdomen） and 31 from UV-exposed areas （neck, back of hands, forehead or face）. Nuclear and mitochondrial DNA was extracted from these samples. Conventional PCR was performed to detect the incidence of 4977 bp and 3895 bp mtDNA deletion. Then, SYBR Green real-time PCR was applied to quantitatively analyze the target mutations in positive samples. Results Conventional PCR showed that the incidence of both 4977 bp deletion and 3895 bp deletion increased with age. For example, the incidence of 4977 bp deletion and 3895 bp deletion accounted for 47.5％ （19/40） and 30％ （12/40）, respectively in samples from volunteers older than 40 years, significantly higher than that in those from volunteers younger than 40 years （χ2 = 4.673, 6.118, respectively, both P < 0.05). The total incidence of 4977 bp deletion and 3895 bp deletion in UV-exposed areas was 48.4％ （15/31） and 32.3% （9/31）, respectively, which did not differ from those in UV-protected areas. The results from real-time PCR revealed a positive correlation of the copy number of 4977 bp deletion and 3895 bp deletion with age （rs = 0.907, 0.845, respectively, both P < 0.05）. When the UV-exposed area was compared with the UV-protected area, no significant difference was found in the copy number of 4977 bp deletion （P = 0.264）, whereas a higher level of 3895 bp deletion was noticed in UV-exposed area（P = 0.014）. Conclusions The 4977 bp mtDNA deletion is primarily associated with chronological aging, and might serve as a biomarker for the process of chronological aging of skin. Deletion of 3895 bp mtDNA seems to be more susceptible to ultraviolet radiation.

Key words: Mitochondrial DNA, mutation, aging